The invention described herein is generally related to acoustic and thermal transducers.
Analyses directed to the measurement of acoustic characteristics in various environments have previously relied primarily on the use of conventional acoustic transducers to measure the power density level and directional characteristics of sound. Such analyses typically involve the measurement of such acoustic characteristics as dynamic pressure and dynamic pressure gradient at different points in space, to determine the optimum design for a given structure for purposes of noise suppression, sound transmission, or for other purposes.
The outputs of conventional acoustic transducers can be combined and processed to determine what is known as the real acoustic power density level, or the acoustic intensity, in a gas or other fluid. There is however another variable, known as the reactive acoustic power density, which is different from real acoustic power density and which may provide additional useful information relating to the acoustic characteristics of various environments. The difference between real and reactive acoustic power density is discussed below. It is sufficient to note here that there has not been previously available any single sensor or transducer for directly measuring either the real or the reactive acoustic power density in a fluid.
The present invention is based on a phenomenon which has been studied by the applicants and which underlies the operation of a class of devices previously disclosed by the applicants in their U.S. Pat. Nos. 4,398,398 and 4,489,553 which are hereby incorporated by reference in the papers "Experiments With an Intrinsically Irreversible Acoustic Heat Engine," J. Wheatley et al., Phys, Rev. Lett. 50, 499 (1983) and "An Intrinsically Irreversible Thermoacoustic Heat Engine," J. Wheatley et al., J. Acoustical Soc. Am. 74, 153 (1983). The phenomenon is a heat transfer process which is intrinsically irreversible in the thermodynamic sense. In practical application, the phenomenon is a heat transfer process by which acoustic energy in a fluid medium produces a temperature gradient and a resultant heat flow in a second medium which is in imperfect thermal contact with the fluid medium. As disclosed and claimed in the above-referenced patent applications, the phenomenon can be utilized, for example, to produce an acoustically driven heat pump which has no moving mechanical parts.
Although the phenomenon is based on a heat transfer process which is intrinsically irreversible in the thermodynamic sense, the process is functionally reversible in practical application, thus also realizing the production of a heat engine that operates at acoustic frequencies and which also has no moving mechanical parts. The present invention represents yet another practical application of the intrinsically irreversible heat transfer phenomenon, which application is generally related to and yet altogether distinct from the above-mentioned applications.